Biocompatible magnetic micro/nanoparticles are currently being developed as targeted drug and gene delivery agents, magnetic resonance imaging contrast agents and as thermoablation mechanisms. However, the potential of magnetic particles for medical applications has not been fully realized due to limitations in the capability to accurately control the movement of the particles in vivo and to adequately concentrate the particles at the target site. For many applications the magnetic particles must migrate through soft tissue under the influence of an applied field to reach the desired location. A better understanding of the factors that influence the movement of magnetic nanoparticles (MNP) through soft tissue is required to fully exploit the potential of these particles. The purpose of this project, therefore, is to characterize the movement of magnetic nano-particles through soft tissues. Our hypothesis is that the movement of MNPs through soft tissues is dependent on the size and shape of the MNPs, the characteristics of the applied magnetic field and the properties of the tissues through which the particles move. In investigate this hypothesis we propose the following specific aims: Aim 1: To formulate and characterize a family of superparamagnetic nanoparticles with variable characteristics. Aim 2: Investigate the effects of MNP characteristics and varying magnetic fields on MNP mobility in viscous liquid and gel. Aim 3: Investigate the effects of visco-elastic properties of matrices (including soft tissue models composed of pure gels and gels with 3D embedded cell cultures) on MNP mobility. Clinical relevance: The data obtained in the proposed studies will significantly contribute to our understanding of the magnetically mediated transport of particles through soft tissues. This information will provide the basis for further development of therapeutic and diagnostic applications of MNPs including targeted therapies, thermal ablation, and MRI contrast agents.